Update ConnectionEventTracker to check if there is an in progress attempt.

google_apis/gcm/engine/connection_event_tracker.cc

Index: google_apis/gcm/engine/connection_event_tracker.cc
diff --git a/google_apis/gcm/engine/connection_event_tracker.cc b/google_apis/gcm/engine/connection_event_tracker.cc
index cad77ebd37e1387c8c24e1fadc0d7ca85401beaa..1f2671ab9cedc05613272fcbb591933da1a31942 100644
--- a/google_apis/gcm/engine/connection_event_tracker.cc
+++ b/google_apis/gcm/engine/connection_event_tracker.cc
@@ -21,6 +21,10 @@ ConnectionEventTracker::ConnectionEventTracker() = default;
 
 ConnectionEventTracker::~ConnectionEventTracker() = default;
 
+bool ConnectionEventTracker::EventInProgress() {
+  return current_event_.has_time_connection_started_ms();
+}
+
 void ConnectionEventTracker::StartConnectionAttempt() {
   // TODO(harkness): Can we dcheck here that there is not an in progress
   // connection?
@@ -32,14 +36,17 @@ void ConnectionEventTracker::StartConnectionAttempt() {
 }
 
 void ConnectionEventTracker::EndConnectionAttempt() {
-  // TODO(harkness): Modify tests so that we can put a DCHECK here.
+  // EndConnectionAttempt should only be called if there was a previous
+  // StartConnectionAttempt.

[Peter Beverloo, 2017/01/12 16:03:27]

optional nit: I'd drop the comment - that's obvious from the DCHECK

[harkness, 2017/01/16 12:20:37]

Done.

+  DCHECK(EventInProgress());
+
   if (completed_events_.size() == kMaxClientEvents) {
     // Don't let the completed events grow beyond the max.
     completed_events_.pop_front();
     number_discarded_events_++;
   }
 
-  // Current event is now completed, so add it to our list of completed events.
+  // Current event is finished, so add it to our list of completed events.
   current_event_.set_time_connection_ended_ms(base::Time::Now().ToJavaTime());
   completed_events_.push_back(current_event_);
   current_event_.Clear();